Offshore wind turbine design - Wind Power Generation and Wind Turbine Design - page 380

need of hammering and hence the heavy vessel. It is not only limited to monopiles
but also can be easily extended to tethered foundations. Thus the costs could
be reduced for both very deep sea wind power plants and the close to shore
monopole-based wind power plant developments.
5.1.3 Tethered foundations
Tethered foundations are often used in oil and gas installations for water depth
exceeding 100 m. Tethered foundations are quite scalable with water depth.
However, their usage in wind power plants does present challenges particularly in
the severe lateral loads, which is common in wind turbines and could affect over-
all system stability. Using ballasts and damping methods counters the lateral load
with the risk of increasing the total cost to a level higher than the seabed-mounted
foundations. This is particularly true at the lower water depths.
There are two types of tethered foundations for potential offshore wind
applications.
1. Tension leg platforms (TLP) : With the TLPs, the hull and the tendon design is
highly coupled since their natural frequencies are not signifi cantly distinct. TLP
stability comes from the buoyancy of the hull, which provides extra tension in
the tendons and consequently provides adequate horizontal stiffness. TLPs as
Figure 10 : Tension leg platform [ 15 ].